Membrane Biofilm Reactor (MBfR)
Biological denitrification is relatively inexpensive and the final waste product is innocuous nitrogen gas. Perchlorate reduction can be performed using the same or different organisms, and the final waste product is chloride. While well-studied for waste-water treatment, there is relatively little information available regarding the use of biological denitrification and perchlorate reduction for producing drinking water.
Biological denitrification and perchlorate reduction are typically performed on a biofilm formed in a membrane biofilm reactor (MBfR) device, which provide a large surface area for the biofilm and means for contacting the biofilm with liquid and/or gas nutrients and electron donors. MBfR devices support the growth of slow-growing bacteria, such as autotrophs, and are particularly efficient in removing contaminants present at low concentrations, and in removing contaminants to nearly undetectable levels, as required for drinking water applications.
Where the levels of electron donors present in the ground-water are too low to support complete biological denitrification or perchlorate reduction, an organic electron donor (in the case of heterotrophic denitrification) or an inorganic donor (in the case of autotrophic denitrification) can be added to MBfR device for utilization by the biofilm. In the cases of biological denitrification and perchlorate reduction, the electron donor is often hydrogen gas (H2), which is supplied to the biomass via hollow membranes upon which the biofilm forms.
While, biological denitrification and perchlorate reduction have both been performed in MBfR devices, the different redox potentials of these oxidized contaminants, as well as other oxidized contaminants that may be present in the ground water, has heretofore resulted in the sequential oxidation of contaminants based on their redox potential, often resulting in residual levels of toxic compounds with comparatively low redox potentials. Such effluent water is unsuitable for use as drinking water without further treatment to reduce the levels of these residual contaminants.
The need exists for more efficient apparatus and methods for removing oxidized contaminants from ground water using MBfR technology, preferably apparatus and methods capable of simultaneous reduction of a variety of contaminants using a single MBfR device.